L-Menthol alleviates cigarette smoke extract induced lung injury in rats by inhibiting oxidative stress and inflammation via nuclear factor kappa B, p38 MAPK and Nrf2 signalling pathways

l-Menthol is the main ingredient of peppermint which affects various pharmacological effects such as anti-inflammation and anti-oxidative activity. In this study, we aimed to evaluate the potential effects of l-menthol on cigarette smoke extract (CSE) induced lung injury in rats. Morphology assessment results revealed that administration with l-menthol (5, 10 or 20 mg kg^-1 d^-1) significantly alleviated CSE-induced lung injury. Besides, l-menthol significantly reduced the inflammatory response by suppressing the production of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6) via downregulating nuclear factor kappa B (NF-κB) and p38 MAPK pathways. Meanwhile, l-menthol decreased the levels of oxidative stress markers including malondialdehyde (MDA) and myeloperoxidase (MPO) whereas it increased the amount of glutathione (GSH), glutathione peroxidase (GSH-Px), superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) through activation of the Nrf2 pathway. Furthermore, the expression of MMP-9 and TIMP-1 in lungs was reduced after treatment with l-menthol, and this indicated that l-menthol might have a potential effect on airway remodeling. Moreover, immunohistochemistry analyses indicated that l-menthol could suppress the infiltration of CD4⁺ and CD8⁺ T cells in lung tissues and this was probably due to the immune regulation activity of l-menthol. Taken together, our findings support that l-menthol might be a potential candidate for the treatment of CSE-induced lung injury in rats.

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